JP2010143494A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device for adequately determining the condition of reverse input. <P>SOLUTION: When a q-axis command current Iq* and a q-axis actual current Iq are input and their current difference ΔIq(¾Iq*¾-¾Iq¾) exceeds a determination reference value Iref, reverse input from a tire is determined to work. Additionally, when the condition that steering torque T detected by a steering torque sensor 22 is greater than reference torque Tref is continued for a reference time or longer, the reverse input from the tire is determined to work. Additionally, when a steering speed ω is calculated in accordance with a rotating angle θm detected by a rotating angle sensor 21 and the steering speed ω exceeds a determination reference value ωref, the reverse input from the tire is determined to work. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering apparatus that drives and controls an electric motor based on a steering operation of a driver to generate a steering assist torque.

  2. Description of the Related Art Conventionally, an electric power steering apparatus is known as an apparatus that assists a driver's steering operation by transmitting output torque of an electric motor to a steering shaft or a rack bar of a steering mechanism. In such an electric power steering device, a target current is calculated based on a steering operation performed by a driver, and energization of the electric motor is controlled so that the calculated target current is obtained.

  When a large force is applied from the tire to the steering mechanism, for example, in a case where the tire collides with a curb while the vehicle is running, the steered wheel turns and a large axial force acts on the rack bar. As a result, the rack bar moves in the axial direction and the steering shaft connected to the rack bar rotates. A state in which reverse input is applied to the steering mechanism from the tire and the steered wheels are steered is referred to as a reverse input state. When the reverse input is large, the rack end member provided at the tip of the rack bar collides with a stopper formed on the rack housing, and an impact force acts on the steering mechanism.

Therefore, for example, in the electric power steering device proposed in Patent Document 1, it is determined whether or not the reverse input state is set, and when it is determined that the reverse input state is set, the steering assist is performed in a direction opposite to the reverse input. The motor is driven to reduce the deterioration of steering feeling. In this electric power steering device, the input side angular velocity ω1 and the output side angular velocity ω2 are detected across the torsion bar of the steering shaft. If the vehicle speed is relatively high and the angular velocity ω2 is larger than the angular velocity ω1, The input state is determined.
JP 2002-29431 A

  However, in the electric power steering device proposed in Patent Document 1, it is difficult to appropriately determine the reverse input state.

  An object of the present invention is to cope with the above problem, and is to appropriately determine a reverse input state.

In order to achieve the above object, the present invention is characterized by an electric motor that is provided in a steering mechanism and generates a steering assist torque, and a steering torque that detects a torsional force acting on a steering shaft connected to a steering handle as a steering torque. Steering by means of detection means, motor control means for calculating a target current based on the detected steering torque, and controlling energization of the electric motor so that the calculated target current flows to the electric motor, and reverse input from the tire Electric power steering system comprising reverse input state detecting means for detecting a reverse input state in which a wheel is steered, and impact reducing means for reducing an impact acting on the steering mechanism when the reverse input state is detected In the device
The reverse input detection means includes: current information acquisition means for acquiring information indicating the target current and information indicating the actual current actually output to the electric motor; and the actual current based on the acquired information. Is smaller than the target current, and when the difference exceeds a determination reference value, current determination means for determining the reverse input state is provided.

  In the present invention, the motor control means calculates the target current based on the steering torque detected by the steering torque detection means, and energizes the electric motor with the calculated target current to generate the steering assist torque. The steering torque detecting means detects, as a steering torque, a torque by which the steering shaft is twisted by a steering operation.

  The reverse input state detection means detects a reverse input state in which the steered wheels are steered by the reverse input from the tire. This reverse input state is a state in which the steered wheels are steered by a strong external force regardless of the driver's steering operation or the steering assist of the electric motor, such as a case where the tire of the steered wheels collides with the curb. It means (a state where the steering shaft or the electric motor rotates), and does not include a state where a weak external force that can be maintained by the driver like the self-aligning torque is applied. The impact reducing means reduces the impact acting on the steering mechanism when a reverse input state is detected.

  The reverse input detection means includes a current information acquisition means and a current determination means in order to properly detect the reverse input state. The current information acquisition means acquires information representing the target current calculated by the motor control means for performing energization control of the electric motor, and information representing the actual current actually output (flowed) to the electric motor. For the actual current, for example, information detected by a current sensor that detects the energization amount of the electric motor may be acquired. Based on this information, the current determination unit determines that the current is in the reverse input state when the actual current is smaller than the target current and the difference exceeds the determination reference value.

  When a reverse input acts on the steering mechanism due to a curb collision of a tire or the like, the steered wheels are steered, and the steering shaft rotates while being abruptly twisted accordingly. The reason why the steering shaft is twisted is that the steering wheel side rotates later than the wheel side (output side) of the steering shaft due to the inertia of the steering wheel. The motor control means detects the twist of the steering shaft as a steering torque, calculates a high target current corresponding to the torsion force, and energizes the electric motor according to the target current.

  At this time, since the steering shaft rotates at a high speed that is not assumed in normal steering operation, a phase delay occurs in the energization control of the electric motor by the motor control means, and the actual current actually output to the electric motor is the target. It cannot follow the current and becomes a low value.

  Therefore, the reverse input detection means uses the current determination means to determine that it is in the reverse input state when the actual current is smaller than the target current and the difference exceeds the determination reference value. Therefore, the reverse input state can be properly determined.

  Another feature of the present invention is that, based on the acquired information, the reverse input detection means further includes torque information acquisition means for acquiring information representing the steering torque detected by the steering torque detection means, and Torque determination means for determining that the steering wheel is in the reverse input state when the steering torque continues for a reference time at a value larger than a reference torque set to a large value that is not detected by the driver's steering operation. It is in.

  When a reverse input acts on the steering mechanism due to a curb collision of a tire or the like, the steered wheels are steered, and accordingly, the steering shaft is rapidly twisted. This torsional force is detected as a steering torque by the steering torque detecting means, but becomes a very large value that is not detected by a normal steering operation. Therefore, the reverse input detection means detects such an event and determines the reverse input state by the torque information acquisition means and the torque determination means. That is, the torque information acquisition unit acquires information representing the steering torque detected by the steering torque detection unit, and the torque determination unit determines that the steering torque is greater than the reference torque set to a large value that is not detected by the driver's steering operation. If it continues for more than the reference time with a large value, it is determined that the state is the reverse input state.

  Therefore, according to the present invention, since the reverse input state is determined based on both the current determination unit and the torque determination unit, the determination accuracy is further improved. For example, if it is determined that either the current determination means or the torque determination means is in the reverse input state, the reverse input state is detected if the reverse input detection means outputs a detection result indicating that the reverse input state is present. There is no delay. Further, when it is determined that both the current determination means and the torque determination means are in the reverse input state, the reverse input state is reliably detected if the detection result that the reverse input detection means is in the reverse input state is output. be able to. As a result, the impact acting on the steering mechanism can be satisfactorily reduced by the impact reducing means.

  According to another aspect of the present invention, the reverse input detection means further includes a steering speed information acquisition means for acquiring information indicating a steering speed, and the steering speed is determined by the driver's steering operation from the acquired information. And a speed determining means for determining that the reverse input state is established when the speed is higher than a reference speed set at a high speed that cannot be rotated.

  When reverse input acts on the steering mechanism due to a curb collision of the tire or the like, the steering wheel is steered, and the steering shaft rotates accordingly. At this time, the rotation speed of the steering shaft is very large and cannot be rotated by the driver's steering operation. Therefore, the reverse input detection means captures such an event and determines the reverse input state by the steering speed information acquisition means and the speed determination means. That is, when the steering speed information acquisition means acquires information indicating the steering speed, and the speed determination means is larger than the reference speed set at a high speed that cannot be rotated by the driver's steering operation, the reverse input state is established. It is determined that

  Therefore, according to the present invention, since the reverse input state is determined based on the current determination unit and the speed determination unit, or the current determination unit, the speed determination unit, and the torque determination unit, the determination accuracy is further improved. Become. In this case, when it is determined that either the current determination unit or the speed determination unit is in the reverse input state, or when it is determined that both the current determination unit and the speed determination unit are in the reverse input state, A detection result indicating that the reverse input detection means is in the reverse input state is output. Further, when the reverse input state is determined based on the current determination unit, the speed determination unit, and the torque determination unit, when it is determined that one of the three determination units is in the reverse input state, or When it is determined that three or two of the current determination unit, speed determination unit, and torque determination unit are in the reverse input state, the detection result indicating that the reverse input detection unit is in the reverse input state is output. Therefore, since the reverse input state can be detected well, the impact acting on the steering mechanism can be satisfactorily reduced by the impact reducing means. Note that the steering speed information can be acquired not only by the rotational angular speed of the steering shaft but also by detecting the rotational angular speed of the electric motor.

  Hereinafter, an electric power steering apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an electric power steering apparatus for a vehicle according to the embodiment.

  This electric power steering apparatus includes a steering mechanism 10 that steers the left front wheel Wfl and the right front wheel Wfr that are steering wheels by a steering operation of the steering handle 11, and an electric motor 20 that is assembled to the steering mechanism 10 and generates a steering assist torque. And a motor drive circuit 30 for driving the electric motor 20 and an electronic control device 100 for controlling the operation of the electric motor 20 as main parts. Hereinafter, the electronic control device 100 is referred to as an assist ECU 100.

  The steering mechanism 10 converts the rotation around the axis of the steering shaft 12 in conjunction with the turning operation of the steering handle 11 into the left and right stroke motion of the rack bar 14 by the rack and pinion mechanism 13. The left front wheel Wfl and the right front wheel Wfr are steered by movement. The steering shaft 12 includes a main shaft 12a connected to the upper end of the steering handle 11, a pinion shaft 12c connected to the rack and pinion mechanism 13, and a main shaft 12a and a pinion shaft 12c connected via universal joints 12d and 12e. And an intermediate shaft 12b.

  The rack bar 14 has a gear portion 14 a housed in the rack housing 15, and both left and right ends thereof are exposed from the rack housing 15 and connected to the tie rod 16. The other ends of the left and right tie rods 16 are connected to knuckles 17 provided on the left and right front wheels Wfl and Wfr. A rack end member 18 is provided at a connection portion between the rack bar 14 and the tie rod 16. On the other hand, stopper portions 15 a are formed at both ends of the rack housing 15. The rack bar 14 is mechanically limited in the range of left and right stroke movement by the contact between the rack end member 18 and the stopper portion 15a. Hereinafter, the position where the movement of the rack bar 14 is restricted by the stopper portion 15a is referred to as a stroke end. Further, the left front wheel Wfl and the right front wheel Wfr are simply referred to as the steering wheel W.

  An electric motor 20 is assembled to the steering shaft 12 (main shaft 12a) via a reduction gear 19. For example, a three-phase brushless motor is used as the electric motor 20. The electric motor 20 rotationally drives the steering shaft 12 around its central axis via the reduction gear 19 by the rotation of the rotor, and applies assist torque to the turning operation of the steering handle 11.

  The electric motor 20 is provided with a motor rotation angle sensor 21. The motor rotation angle sensor 21 is constituted by, for example, a resolver, and outputs a detection signal indicating the rotation angle θm of the rotor of the electric motor 20. The motor rotation angle θm is used for calculating the electrical angle θe of the electric motor 20. Hereinafter, the motor rotation angle sensor 21 is simply referred to as a rotation angle sensor 21.

  Since the electric motor 20 and the steering shaft 12 are connected via the reduction gear 19, the motor rotation angle θm detected by the rotation angle sensor 21 corresponds to the steering angle of the steering handle 11. Therefore, the rotation angle sensor 21 is not only used for detecting the electrical angle θe of the electric motor 20 but also used as a steering angle detection sensor. Hereinafter, the steering angle corresponding to the rotation angle based on the steering angle neutral point is referred to as a steering angle θh. Further, the steering speed, which is the rotational speed of the steering shaft 12, can be obtained by time-differentiating the motor rotation angle θm or the steering angle θh. Hereinafter, the steering speed calculated in this way is referred to as a steering speed ω. As for the steering angle θh, the steering angle in the right direction with respect to the reference rudder angle neutral point is expressed as a positive value, and the steering angle in the left direction with respect to the reference rudder angle neutral point is expressed as a negative value. In addition, the steering speed ω represents a steering speed when the steering handle 11 is rotating in the right direction as a positive value and a steering speed when the steering handle 11 is rotated in the left direction as a negative value. To. Further, when discussing the magnitude of the steering angle and the steering speed, the absolute values are used.

  A steering torque sensor 22 is provided between the steering handle 11 and the reduction gear 21 on the steering shaft 12 (main shaft 12a). The steering torque sensor 22 detects a torsional force acting on a torsion bar (not shown) interposed in the steering shaft 12 (main shaft 12a) as a steering torque T applied to the steering handle 11. For example, resolvers are provided at both ends of the torsion bar, and the steering torque T is detected based on the difference in rotational angle detected by the two resolvers.

  The steering torque T is a positive value for torque acting in the clockwise direction on the steering shaft 12 (torque in a torsional state where the upper portion of the torsion bar is in the right rotational position relative to the lower portion). (Torque in a torsional state where the upper part of the torsion bar is in the left rotation position relative to the lower part) is expressed by a negative value. When discussing the magnitude of the steering torque, the absolute value is used.

  The motor drive circuit 30 comprises a three-phase inverter circuit composed of six switching elements 31 to 36 made of MOS-FET (Metal Oxide Semiconductor Field Effect Transistor). Specifically, an upper arm circuit in which a first switching element 31, a third switching element 33, and a fifth switching element 35 are provided in parallel, a second switching element 32, a fourth switching element 34, and a sixth switching element 36 are provided. A configuration is adopted in which a lower arm circuit provided in parallel is connected in series and a power supply line 37 to the electric motor 20 is drawn from between the upper and lower arm circuits.

  The motor drive circuit 30 is provided with a current sensor 38 that detects a current flowing through the electric motor 20. The current sensor 38 detects the current flowing in each phase (U phase, V phase, W phase) and outputs a detection signal corresponding to the detected current value to the assist ECU 100. Hereinafter, the measured three-phase current values are collectively referred to as a motor current Iuvw.

  As for each switching element 31-36 of the motor drive circuit 30, a gate is connected to assist ECU100, respectively, and a duty ratio is controlled by the PWM control signal output from assist ECU100. Thereby, the drive voltage of the electric motor 20 is adjusted to the target voltage. Incidentally, as indicated by circuit symbols in the figure, the MOSFETs constituting the switching elements 31 to 36 are parasitically structured with diodes.

  The assist ECU 100 includes a microcomputer including a CPU, a ROM, a RAM, and the like as a main part. The assist ECU 100 is connected to a rotation angle sensor 21, a steering torque sensor 22, a current sensor 38, and a vehicle speed sensor 25 that detects the vehicle speed, and a detection signal representing the motor rotation angle θm, the steering torque T, the motor current Iuvw, and the vehicle speed v. Enter. Then, based on the input detection signal, a command current (target current) to be passed through the electric motor 20 is calculated so as to obtain an optimum steering assist torque according to the driver's steering operation so that the command current flows. The duty ratio of each switching element 31 to 36 of the motor drive circuit 30 is controlled.

  Further, the assist ECU 100 detects a reverse input state in which the steered wheels W are steered by reverse input from the tire, and the steering mechanism 10 (particularly, the steering shaft 12) detects the reverse input state. It also has a function to reduce the working impact. The function of the assist ECU 100 will be described later.

  Next, a power supply system of the electric power steering apparatus will be described. The electric power steering device is supplied with power from an in-vehicle power supply device 80. The in-vehicle power supply device 80 is configured by connecting in parallel a main battery 81 that is a general in-vehicle battery having a rated output voltage of 12V and an alternator 82 having a rated output voltage of 14V that is generated by the rotation of the engine. A power supply source line 83 and a ground line 84 are connected to the in-vehicle power supply device 80. The power supply source line 83 branches into a control system power line 85 and a drive system power line 86. The control system power supply line 85 functions as a power supply line for supplying power to the assist ECU 100. The drive system power supply line 86 functions as a power supply line that supplies power to both the motor drive circuit 30 and the assist ECU 100.

  An ignition switch 87 is connected to the control system power supply line 85. A main power relay 88 is connected to the drive system power line 86. The main power supply relay 88 closes the contact by an on signal from the assist ECU 100 to form a power supply circuit to the electric motor 20, and opens the contact by an off signal to cut off the power supply circuit to the electric motor 20. is there. The control system power supply line 85 is connected to the power supply + terminal of the assist ECU 100, and includes a diode 89 on the load side (assist ECU 100 side) from the ignition switch 87 in the middle. The diode 89 is a backflow prevention element that is provided with the cathode facing the assist ECU 100 and the anode facing the in-vehicle power supply device 80, and allows energization only in the power supply direction.

  The drive system power line 86 is provided with a connecting line 90 branched from the main power relay 88 and connected to the control system power line 85 on the load side. This connection line 90 is connected to the assist ECU 100 side from the connection position of the diode 89 in the control system power supply line 85. A diode 91 is connected to the connecting line 90. The diode 91 is provided with the cathode facing the control system power line 85 side and the anode facing the drive system power line 86 side. Therefore, the circuit configuration is such that power can be supplied from the drive system power supply line 86 to the control system power supply line 85 via the connection line 91, but power cannot be supplied from the control system power supply line 85 to the drive system power supply line 86. . The drive system power supply line 86 and the ground line 84 are connected to the power supply input section of the motor drive circuit 30. The ground line 84 is also connected to the ground terminal of the assist ECU 100.

  Next, functions of the assist ECU 100 will be described with reference to FIG. FIG. 2 is a functional block diagram showing functions processed by program control of the microcomputer of the assist ECU 100.

  As shown in FIG. 2, the assist ECU 100 includes an assist current command unit 101. The assist command unit 101 switches the control mode between when the reverse input state is not detected by the reverse input state determination unit 110 described later (normal time) and after the reverse input state is detected. First, the control mode in normal time will be described. As shown in FIG. 3, the assist current command unit 101 stores a basic assist torque table for setting the basic assist torque Tas according to the steering torque T and the vehicle speed v. The assist current command unit 101 inputs the steering torque T output from the steering torque sensor 22 and the vehicle speed v output from the vehicle speed sensor 25, and calculates the basic assist torque Tas by referring to this basic assist torque table. . The basic assist torque Tas is set to increase as the steering torque T increases and to decrease as the vehicle speed v increases. FIG. 3 shows the assist torque table when steering in the right direction. However, when steering in the left direction, the magnitude of the assist torque table is the same except that the direction of the basic assist torque Tas is different.

  The assist current command unit 101 also converts the motor rotation angle θm detected by the rotation angle sensor 21 into an angle based on the steering angle neutral point, and the steering speed obtained by time-differentiating the motor rotation angle θm. ω is calculated, and using these, a compensation value Tc for the basic assist torque Tas is calculated. The compensation value Tc is, for example, a return torque corresponding to a return force to the basic position of the steering shaft 12 that increases in proportion to the steering angle θh and a resistance force to the rotation of the steering shaft 12 that increases in proportion to the steering speed ω. Is calculated as the sum of The assist current command unit 101 sets the sum of the calculated basic assist torque Tas and the compensation value Tc as the target assist torque T *, and divides the target assist torque T * by the torque constant, thereby obtaining the dq coordinate system. A q-axis command current Iq * is calculated.

  When performing three-phase energization control, the assist ECU 100 is electrically controlled by vector control described in a dq coordinate system in which the rotation direction of the electric motor 20 is the q axis and the direction orthogonal to the rotation direction is the d axis. The rotation of the motor 20 is controlled. The q-axis current generates torque in the electric motor 20, but the d-axis current does not generate torque in the electric motor 20, but is used for field control. The assist current command unit 101 in this embodiment sets the d-axis command current Id * to zero (Id * = 0) unless a reverse input state is detected.

  The q-axis command current Iq * and the d-axis command current Id * calculated in this way are output to the feedback control unit 102. The feedback control unit 102 calculates a deviation ΔIq obtained by subtracting the q-axis actual current Iq from the q-axis command current Iq *, and the q-axis actual current Iq is changed to the q-axis command current Iq * by proportional-integral control using the deviation ΔIq. The q-axis command voltage Vq * is calculated so as to follow. Similarly, a deviation ΔId obtained by subtracting the d-axis actual current Id from the d-axis command current Id * is calculated, and the d-axis actual current Id follows the d-axis command current Id * by proportional-integral control using the deviation ΔId. D-axis command voltage Vd * is calculated.

  The q-axis actual current Iq and the d-axis actual current Id are obtained by converting the detected values Iu, Iv, and Iw of the three-phase current actually flowing in the coil of the electric motor 20 into the two-phase current in the dq coordinate system. . Conversion from the three-phase currents Iu, Iv, and Iw to the two-phase currents Id and Iq in the dq coordinate system is performed by the three-phase / two-phase conversion unit 103. The three-phase / two-phase conversion unit 103 inputs the motor electrical angle θe output from the rotation angle conversion unit 104, and based on the motor electrical angle θe, the three-phase currents Iu, Iv, Iw is converted into two-phase currents Id and Iq in the dq coordinate system. The rotation angle conversion unit 104 calculates the motor electrical angle θe based on the rotation angle θm output from the rotation angle sensor 21.

  The q-axis command voltage Vq * and the d-axis command voltage Vd * calculated by the feedback control unit 102 are output to the 2-phase / 3-phase coordinate conversion unit 105. The two-phase / three-phase coordinate conversion unit 105 converts the q-axis command voltage Vq * and the d-axis command voltage Vd * into the three-phase command voltages Vu * and Vv * based on the electrical angle θe output from the rotation angle conversion unit 104. , Vw *, and the converted three-phase command voltages Vu *, Vv *, Vw * are output to the PWM signal generator 106. The PWM signal generator 106 outputs PWM control signals corresponding to the three-phase command voltages Vu *, Vv *, Vw * to the switching elements 31 to 36 of the motor drive circuit 30. As a result, the electric motor 20 is driven, and a steering assist torque that follows the target assist torque T * is applied to the steering mechanism 10.

  Next, the reverse input state detection function will be described. When a large reverse input is applied to the steering mechanism 10 due to a tire curb collision or the like, the steering wheel W is steered, and the steering shaft 12 is rapidly twisted accordingly. This is because the steering handle 12 side (input side) rotates later than the rack bar 14 side (output side) of the steering shaft 12 due to the inertia of the steering handle 11 and the inertia of the electric motor 20. The steering shaft 12 rotates at a high speed by rapidly increasing the rotation speed while strongly twisting the torsion bar.

  Immediately after the occurrence of such reverse input, the assist current command unit 101 increases the q-axis command current Iq * as the steering torque T (torsion torque of the torsion bar) increases rapidly. However, since the steering shaft 12 rotates at a high speed that is not assumed in normal steering operation, the change in the electrical angle θe is too fast, causing a phase delay in the energization control of the electric motor 20 by the assist ECU 100. Therefore, as shown in FIG. 4, the current that should flow in the q-axis direction, which is the direction of torque generation, is shifted in the d-axis direction, and the q-axis actual current Iq that can actually be output to the electric motor 20 is reduced. As a result, as shown in FIG. 5, the q-axis actual current Iq decreases with respect to the q-axis command current Iq * from time t1 when the rotation speed of the steering shaft 12 becomes very high. FIG. 5 shows the transition of the q-axis command current Iq * and the q-axis actual current Iq immediately after the reverse input occurs.

  Therefore, the assist ECU 100 includes a reverse input state determination unit 110 as shown in FIG. 2, and detects the reverse input state by capturing such a phenomenon.

  Here, the process of the reverse input state determination unit 110 will be described using a flowchart. FIG. 6 is a flowchart showing a reverse input determination routine executed by the reverse input determination unit 110. The reverse input determination routine is stored in the ROM of the assist ECU 100 as a control program. The assist ECU 100 starts the steering assist control described above after making an initial diagnosis by turning on the ignition switch 87, and this reverse input determination routine is also started in parallel therewith and is repeated at a predetermined short cycle.

When the reverse input determination routine is started, the reverse input state determination unit 110, in step S11, q-axis command current Iq * output from the assist current command unit 101 and q output from the three-phase / two-phase conversion unit 103. Read the actual shaft current Iq. That is, the target current and actual current in the q axis are read. Subsequently, in step S12, a current difference ΔIq which is a difference in current value is calculated. This current difference ΔIq is calculated by the following equation.
ΔIq = | Iq * | − | Iq |
The q-axis current is a positive value for a current flowing so as to generate a right steering torque in the electric motor 20, and a negative value for a current flowing so as to generate a left steering torque. Therefore, here, in order to compare the magnitudes of the current values, the current difference ΔIq is calculated using the absolute value.

  Subsequently, in step S13, it is determined whether or not the current difference ΔIq is larger than a determination reference value Iref (positive value). When no reverse input occurs, the difference between the q-axis command current Iq * and the q-axis actual current Iq is small by current feedback control. However, when reverse input occurs, the steering shaft 12 rotates at a high speed as described above, and therefore the q-axis actual current Iq decreases as the q-axis command current Iq * increases. Therefore, the magnitude | Iq | of the q-axis actual current Iq is smaller than the magnitude | Iq * | of the q-axis command current Iq *, and the difference therebetween is large. Therefore, the reverse input state determination unit 110 determines whether reverse input has occurred based on the magnitude of the current difference ΔIq.

  When the current difference ΔIq is equal to or smaller than the determination reference value Iref, the reverse input state determination unit 110 determines that no reverse input has occurred in step S14 and sets the reverse input determination flag F to 0 ( F = 0), and outputs the reverse input determination flag F to the assist current command unit 101. Then, the reverse input determination routine is temporarily terminated. The reverse input determination routine is repeatedly executed at a predetermined short cycle. Therefore, during a period in which it is determined that no reverse input has occurred, a signal with the reverse input determination flag F = 0 is output to the assist current command unit 101.

  On the other hand, if the current difference ΔIq exceeds the determination reference value Iref (S13: Yes), it is determined in step S15 that reverse input has occurred, and the reverse input determination flag F is set to 1 (F = 1), the reverse input determination flag F is output to the assist current command unit 101, and this routine is temporarily terminated. Since the reverse input determination routine is repeatedly executed at a predetermined short cycle, a signal of the reverse input determination flag F = 1 is output to the assist current command unit 101 during a period in which it is determined that reverse input has occurred. Will be.

  The assist current command unit 101 switches the control mode according to the determination of the reverse input state determination unit 110. FIG. 7 is a flowchart showing a control mode switching routine executed by the assist current command unit 101. The control mode switching routine is stored as a control program in the ROM of the assist ECU 100. The control mode switching routine is started after initial diagnosis is performed by turning on the ignition switch 87, and is repeated at a predetermined short cycle.

  When this routine is started, the assist current command unit 101 reads the reverse input determination flag F from the reverse input state determination unit 110 in step S21. Subsequently, in step S22, it is determined whether or not the reverse input determination flag F is set to 1 (F = 1). When the reverse input determination flag F is set to 0 (F = 0), that is, when the reverse input state is not set, in step S23, the control mode is set to output a current command value for normal steering assist control. Therefore, as described above, the assist current command unit 101 calculates the basic assist torque Tas from the steering torque T and the vehicle speed v, and calculates the compensation value Tc from the steering angle θh and the steering speed ω, and the sum ( The target assist torque T * is obtained by (Tas + Tc), and the q-axis command current Iq * is calculated by dividing the target assist torque T * by the torque constant. Further, the d-axis command current Id * is set to zero.

  When the assist current command unit 101 outputs the steering assist current command in step S23, the control mode switching routine is temporarily terminated. The control mode switching routine is repeated at a predetermined short cycle. Accordingly, in a period when the reverse input state is not in effect, such calculation of the current command value is repeated, and an appropriate steering assist torque can be obtained by current feedback control.

  On the other hand, when the reverse input determination flag F is set to 1 (S22: Yes), that is, when the reverse input state is detected, the assist current command unit 101 determines the current command for shock reduction in step S24. Is set to the control mode that outputs. In the present embodiment, as shown in FIG. 8, the q-axis command current Iq * is set to zero and the d-axis command current Id * is set in the direction in which the electric motor 20 is locked, that is, in the direction in which the field is increased. Is set to a constant value Idc. In general, the d-axis current is used for field weakening, but in this embodiment, the field is strengthened by flowing in the opposite direction. Therefore, the energization of the electric motor 20 is controlled by the command current (Iq * = 0, Id * = Idc) for reducing the impact, and the brake works against the rotation of the electric motor 20.

  When a strong reverse input is applied to the steering mechanism 10 as in the case where the tire of the steered wheel W collides with the curb, the steered wheel W is steered and the rack bar 14 moves in the axial direction. Thereby, the kinetic energy in the axial direction of the rack bar 14 is transmitted to the steering shaft 12 via the rack and pinion mechanism 13, and the steering shaft 12 rotates. Further, the rotation of the steering shaft 12 rotates the rotor of the electric motor 20 in the same direction. Then, the rack bar 14 reaches the stroke end, and one of the stoppers 18 provided at both ends of the rack bar 14 collides with the end of the rack housing 15. Hereinafter, this collision is referred to as a stroke end collision.

  When a stroke end collision occurs, the rotation of the output side of the steering shaft 12 is restricted by the stop of the rack bar 14. However, since the input side of the steering shaft 12 is open, the steering inertia torque and the motor inertia torque further increase. Rotate. For this reason, at the time of a stroke end collision, the output side of the reduction gear 19 in the steering shaft 12 is twisted and a large impact is applied. In particular, in the column assist system in which the electric motor 20 is connected to the steering shaft 12 via the reduction gear 19 as in the present embodiment, the impact is large because the inertia torque of the electric motor 20 is greatly affected. Therefore, it is necessary to increase the strength of the steering shaft 12 (the strength of the intermediate shaft 12b, the pinion shaft 12c, and the universal joints 12d and 12e connecting them).

  Therefore, in the present embodiment, when the reverse input state is detected, it is immediately switched to the command current for reducing the impact (Iq * = 0, Id * = Idc), and the brake is applied to the rotation of the electric motor 20. Therefore, an increase in the moving speed of the rack bar 14 can be suppressed before reaching the stroke end, and the impact due to the collision can be reduced. FIG. 9 shows the transition of the rotational speed (shaft rotational speed) of the steering shaft 12 when reverse input occurs and the transition of the torque (shaft torque) acting on the steering shaft 12 according to this embodiment. It is a graph showing the case (solid line) and the case where brake braking is not applied (broken line). As shown in the figure, when brake braking is not applied, the motor rotation speed increases, so the impact (shaft torque) at the stroke end collision is large. However, when brake braking is applied, reverse input detection is performed. Thereafter, an increase in the shaft rotation speed can be suppressed, and an impact at the time of stroke end collision can be reduced.

  When the assist current command unit 101 outputs a current command for impact reduction in step S24, the assist current command unit 101 once ends the control mode switching routine. The control mode switching routine is repeated at a predetermined short cycle. Therefore, during the period in which the reverse input state is detected, the brake braking of the electric motor 20 is continued. Note that after detecting the occurrence of such reverse input, a warning lamp (not shown) may be blinked to prompt the driver to check.

  According to the electric power steering apparatus of the present embodiment described above, the determination accuracy is high because the reverse input state is determined based on the current difference ΔIq. Therefore, the impact applied to the steering mechanism 10, particularly the steering shaft 12, can be appropriately reduced. As a result, the durability of the steering mechanism 10 can be improved. Further, the impact transmitted from the steering handle 11 to the driver can be reduced.

Next, another embodiment relating to the processing of the reverse input state determination unit 110 will be described. The embodiment described above is referred to as a first embodiment, and the embodiment described below is referred to as a second embodiment. In FIG. 2, the specific configuration according to the second embodiment is indicated by a broken line.
In the first embodiment, the reverse input state is determined based on the current difference ΔIq. However, in the second embodiment, the reverse input is based not only on the current difference ΔIq but also on the steering torque T and the steering speed ω. Determine the state. FIG. 10 is a flowchart illustrating a reverse input determination routine executed by the reverse input determination unit 110 according to the second embodiment. This reverse input determination routine is executed in parallel with the processing of the assist current command unit 101 and is repeated at a predetermined short cycle.

  When this routine is started, the reverse input state determination unit 110 performs reverse input state determination processing based on the current difference ΔIq in step S10. The process of step S10 is the same as the process of the reverse input determination routine of the embodiment shown in FIG. However, in the processing of steps S14 and S15 described above, the reverse input determination flag is set to Fi, and Fi = 1 when it is determined that reverse input has occurred, and Fi = 0 when it is determined that reverse input has not occurred. Shall be set to

  Subsequently, the reverse input state determination unit 110 determines whether or not the reverse input determination flag Fi is 0 in step S16. When the reverse input determination flag Fi is set to 1 (Fi = 1), that is, when the reverse input state is determined based on the current difference ΔIq, the reverse input determination flag F is determined in step S17. Is set to 1 (F = 1), and the reverse input determination flag F is output to the assist current command unit 101.

  On the other hand, when the reverse input determination flag Fi is set to 0 (Fi = 0), the reverse input determination process based on the steering torque in step S30 is performed. The processing in step S30 is executed according to the subroutine of FIG. First, in step S31, the steering torque T detected by the steering torque sensor 22 is read. Subsequently, it is determined whether or not the magnitude | T | of the steering torque T is larger than a predetermined determination reference torque Tref. The determination reference torque Tref is set to a large value that is not detected by the steering operation by the driver.

  Here, the principle of determining the reverse input state based on the steering torque T will be described. When a reverse input acts on the steering mechanism 10 due to a curb collision of the tire of the steered wheel W, the steered wheel W is steered, and accordingly, the torsion bar of the steering shaft 12 is abruptly twisted. This torsional force is detected by the steering torque sensor 22 as the steering torque T, but is a very large value that is not detected by a normal steering operation. For example, as shown in FIG. 12, the actual torque (shown by a broken line) that acts to twist the torsion bar of the steering shaft 12 exceeds the detectable range of the steering torque sensor 22. Therefore, the detected value T (indicated by the solid line) of the steering torque sensor 22 continues to be maintained at the maximum value. This is a state in which the detected value has been shaken out. Therefore, the reverse input state can be determined by setting the determination reference torque Tref in the vicinity of the maximum value (a value slightly smaller than the maximum value) that can be detected by the steering torque sensor 22.

  If the steering torque | T | is equal to or smaller than the predetermined determination reference torque Tref (S32: No), the reverse input state determination unit 110 clears the timer value t of the timer for time to zero in step S33, and then in step S34. Then, it is determined that no reverse input has occurred, and the reverse input determination flag Ft is set to 0 (Ft = 0), and this subroutine is exited.

  On the other hand, if the steering torque | T | exceeds the preset determination reference torque Tref (S32: Yes), the reverse input state determination unit 110 increments the timer value t of the timer for time by 1 in step S35. In step S36, it is determined whether or not the timer value t has reached the determination reference time tup. The timer value t is set to zero when the reverse input determination routine is started. Accordingly, in this step S36, it is determined whether or not the state where the steering torque | T | exceeds the predetermined determination reference torque Tref continues for the determination reference time tup.

  If the continuous time during which the steering torque | T | exceeds the determination reference torque Tref is less than the determination reference time tup, the reverse input determination flag Ft is set to 0 (Ft = 0) in step S34, and this subroutine is executed. Exit.

  When reverse input occurs, the torque acting on the steering shaft 12 changes at a large value exceeding the detection range of the steering torque sensor 22, for example, as shown by the broken line in FIG. Therefore, the state where the steering torque | T | exceeds the determination reference torque Tref continues. When the continuous time during which the steering torque | T | exceeds the determination reference torque Tref reaches the determination reference time tup (S36: Yes), the reverse input state determination unit 110 determines that a reverse input is generated in step S37. The reverse input determination flag Ft is set to 1 (Ft = 1) and the subroutine is exited.

  If the reverse input determination flag Ft is set in step S34 or step S37, the process proceeds to step S38 in FIG. In step S38, the reverse input state determination unit 110 determines whether or not the reverse input determination flag Ft is zero. If the reverse input determination flag Ft is set to 1 (Ft = 1), that is, if the reverse input state is determined based on the steering torque | T |, the reverse input determination is made in step S17. The flag F is set to 1 (F = 1), and the reverse input determination flag F is output to the assist current command unit 101.

  On the other hand, when the reverse input determination flag Ft is set to 0 (Ft = 0), the reverse input determination process based on the steering speed in step S40 is performed. The process of step S40 is executed according to the subroutine of FIG. First, in step S41, the steering speed ω is read from the steering speed conversion unit 107. As shown by a broken line in FIG. 2, the steering speed conversion unit 107 inputs the motor rotation angle θm output from the rotation angle sensor 21 and calculates the amount of change per unit time of the motor rotation angle θm, that is, time differentiation. Thus, the steering speed ω is calculated. Note that the motor rotation angle θm may be input to the reverse input determination unit 110, and the steering speed ω may be calculated in the reverse input determination unit 110.

  Subsequently, in step S42, the reverse input state determination unit 110 determines whether or not the magnitude | ω | of the steering speed ω exceeds a preset determination reference speed ωref. The determination reference speed ωref is set to a high speed value that cannot be rotated by a steering operation by the driver.

  Here, the principle of determining the reverse input state based on the steering speed ω will be described. When a reverse input is applied to the steering mechanism 10 due to a curb collision of a tire of the steering wheel W or the like, the steering wheel W is steered, and the steering shaft 12 is rotated accordingly. At this time, the rotational speed of the steering shaft 12 is very large and cannot be rotated by the driver's steering operation. FIG. 14 shows the transition of the steering speed when the driver turns the steering wheel 11 quickly and the transition of the steering speed when the reverse input occurs. During the steering operation by the driver, a large steering speed ω is not detected. Therefore, the reverse input state can be determined by setting the determination reference speed ωref to a high speed value that is not detected by the steering operation by the driver.

  If the steering speed | ω | is equal to or lower than the preset determination reference speed ωref (S42: No), the reverse input state determination unit 110 determines that no reverse input has occurred in step S43, and determines the reverse input. The flag Fω is set to 0 (Fω = 0), and this subroutine is exited.

  On the other hand, if the steering speed | ω | exceeds the predetermined determination reference speed ωref (S42: Yes), it is determined in step S44 that reverse input has occurred, and the reverse input determination flag Fω is set to 1. (Fω = 1), and this subroutine is exited.

  If the reverse input determination flag Fω is set in step S43 or step S44, the process proceeds to step S45 in FIG. In step S45, the reverse input state determination unit 110 determines whether or not the reverse input determination flag Fω is zero. If the reverse input determination flag Fω is set to 1 (Fω = 1), that is, if the reverse input state is determined based on the steering speed | ω |, the reverse input determination is made in step S17. The flag F is set to 1 (F = 1), and the reverse input determination flag F is output to the assist current command unit 101.

  On the other hand, if the reverse input determination flag Fω is set to 0 (Fω = 0), the reverse input determination flag F is set to 0 (F = 0) in step S46, and the reverse input determination flag F is set. Output to the assist current command unit 101.

  When the reverse input state determination unit 110 outputs the reverse input determination flag F in step S17 or step S46, the reverse input determination routine is temporarily ended. Then, similar processing is repeated at a predetermined short cycle.

  According to the electric power steering apparatus that executes the reverse input determination routine according to the second embodiment described above, not only the current difference ΔIq but also three changes taking into account the transition of the steering torque | T | and the steering speed | ω | Since the reverse input determination process is performed, the determination accuracy is further improved. Further, when the occurrence of reverse input is detected in any one of the determination processes, a current command for impact reduction is output, so that the impact of the steering mechanism 10 can be more reliably reduced without delay. .

  Regarding the determination of the reverse input state, a configuration in which the reverse input determination processing based on the steering torque is omitted (a configuration in which steps S30 and S38 are omitted), or a configuration in which the reverse input determination processing based on the steering speed is omitted (step S40). , S45 can be omitted).

  In the second embodiment, any one of three reverse input determination processes (a reverse input determination process based on a current difference, a reverse input determination process based on a steering torque, and a reverse input determination process based on a steering speed). When it is determined that at least one reverse input is present, a determination result indicating that it is in the reverse input state is output, but when two or three of the three reverse input determination processes are determined to be reverse input Alternatively, a determination result indicating that the state is the reverse input state may be output. For example, when it is determined that there is a reverse input in both the reverse input determination process based on the current difference and the reverse input determination process based on the steering torque (Fi = 1 and Ft = 1), the reverse input state is indicated. The determination result (F = 1) may be output. Further, when it is determined that there is a reverse input in both the reverse input determination process based on the current difference and the reverse input determination process based on the steering speed (Fi = 1 and Fω = 1), it indicates that the reverse input state is present. The determination result (F = 1) may be output. Further, when it is determined that the reverse input is present in all of the reverse input determination process based on the current difference, the reverse input determination process based on the steering torque, and the reverse input determination process based on the steering speed (Fi = 1, Ft = 1, In addition, Fω = 1), and a determination result (F = 1) indicating that it is in the reverse input state may be output. FIG. 17 is a flowchart showing the third example. In the figure, the same processing as in the second embodiment is indicated by using the same step S code as the step code in FIG. According to this, it is possible to reliably detect the reverse input state.

  Further, in the first and second embodiments and the modified example of the reverse input determination of the second embodiment, it is further determined whether or not the steering direction is away from the neutral position based on the steering speed ω. It may be determined that the steering direction is away from the neutral position as an AND condition for the reverse input determination. In this case, the determination accuracy of the reverse input state is further improved.

  Next, a description will be given of a modification of the calculation process of the command current for impact reduction performed by the assist current command unit 101 when the reverse input state is detected. In the above-described embodiment, when the reverse input state is detected, the q-axis command current Iq * = 0, the d-axis command current Id * = Idc (a constant value in the motor lock direction) as the command current for reducing the impact. However, instead of setting the d-axis command current Id * to a constant value, it may be set so as to change according to the motor rotation speed as shown in FIG. Since the motor rotation speed is proportional to the steering speed ω, the d-axis command current Id * may be set based on the steering speed ω output from the steering speed detection unit 107. In this example, a d-axis command current Id * in the motor lock direction that increases as the motor rotation speed increases is set. According to this, since a larger brake can be generated as the motor rotation speed is faster, more appropriate impact reduction can be performed.

  As another modification, as shown in FIG. 16, the q-axis command current Iq * may be set so as to change according to the motor rotation speed. In this case, the q-axis command current Iq * has a magnitude that increases as the motor rotation speed increases, and in a direction that generates torque in the direction opposite to the direction in which the electric motor 20 rotates due to reverse input. Is set. According to this, since a larger brake can be generated as the motor rotation speed is faster, more appropriate impact reduction can be performed.

  As another modification, when a reverse input state is detected, a brake by power generation may be applied by short-circuiting the three phases (U phase, V phase, W phase) of the electric motor 20. For example, when a reverse input state is detected, the calculation of the command currents id *, iq * is stopped, and the switching elements 31, 33, 35 of the upper arm circuit of the motor drive circuit 30 are turned on (duty ratio 100%), A PWM control signal for turning off the switching elements 32, 34 and 366 of the lower arm circuit (duty ratio 0%) is output to the motor drive circuit 30. As a result, the three phases of the electric motor 20 are short-circuited, and the generated current flows through the motor coil due to the rotation of the rotor by reverse input, and the electric motor 20 is braked.

  The electric power steering apparatus according to the present embodiment has been described above. However, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the object of the present invention.

  For example, in this embodiment, the steering angle θ and the steering speed ω are detected by the rotation angle sensor 21 that detects the rotation angle of the electric motor 20. For example, a rotation angle sensor is provided on the steering shaft 12. The steering angle θ and the steering speed ω may be detected based on the rotation angle and the rotation angular velocity of the steering shaft 12.

  In the present embodiment, the MOS-FET is used as the switching element of the motor drive circuit 30, but other switching elements may be used. In addition, a booster circuit that boosts the power supplied from the in-vehicle power supply device 80 may be provided on the input side of the motor drive circuit 30 to increase the output of the electric motor 20.

1 is a schematic configuration diagram of an electric power steering apparatus according to an embodiment of the present invention. It is a functional block diagram showing the process of the microcomputer of assist ECU. It is a graph showing a basic assist torque table. It is a graph showing the phase delay of q-axis current. It is a graph showing transition of the command current and the actual current in the reverse input state. It is a flowchart showing a reverse input determination routine (1st Embodiment). It is a flowchart showing a control form switching routine. It is a graph showing the change of command current. It is a graph showing the change of the shaft rotational speed and shaft torque in a reverse input state. It is a flowchart showing a reverse input determination routine (2nd Embodiment). It is a flowchart showing the reverse input determination subroutine based on steering torque. It is a graph showing transition of the actual torque and detection torque in a reverse input state. It is a flowchart showing the reverse input determination subroutine based on a steering speed. It is a graph showing transition of the steering speed at the time of normal steering and reverse input. It is a graph showing the setting map of the command current as a modification. It is a graph showing the setting map of the command current as another modification. It is a flowchart showing a reverse input determination routine (modification of 2nd Embodiment).

  DESCRIPTION OF SYMBOLS 10 ... Steering mechanism, 11 ... Steering handle, 12 ... Steering shaft, 20 ... Electric motor, 21 ... Rotation angle sensor, 22 ... Steering torque sensor, 25 ... Vehicle speed sensor, 30 ... Motor drive circuit, 37 ... Electric power supply line, 38 DESCRIPTION OF SYMBOLS ... Current sensor, 88 ... Main power supply relay, 100 ... Electronic control unit (assist ECU), 101 ... Assist current command unit, 102 ... Feedback control unit, 103 ... Three-phase / two-phase conversion unit, 104 ... Rotation angle conversion unit, 105... Three-phase / two-phase coordinate conversion unit 106... PWM control signal generation unit 107 107 Steering speed detection unit 110 110 Reverse input state detection unit

Claims (3)

An electric motor provided in the steering mechanism for generating steering assist torque;
A steering torque detecting means for detecting a torsional force acting on a steering shaft connected to the steering handle as a steering torque;
Motor control means for calculating a target current based on the detected steering torque and controlling energization of the electric motor so that the calculated target current flows to the electric motor;
Reverse input state detection means for detecting a reverse input state in which the steered wheels are steered by reverse input from the tire;
An electric power steering apparatus comprising: an impact reducing means for reducing an impact acting on the steering mechanism when the reverse input state is detected;
The reverse input detection means includes
Current information acquisition means for acquiring information representing the target current and information representing the actual current actually output to the electric motor;
A current determination unit that determines that the reverse input state is established when the actual current is smaller than the target current and a difference thereof exceeds a determination reference value based on the acquired information. Electric power steering device. The reverse input detection means further includes:
Torque information acquisition means for acquiring information representing the steering torque detected by the steering torque detection means;
Based on the acquired information, when the steering torque continues for a reference time at a value larger than a reference torque set to a large value that is not detected by the driver's steering operation, the reverse input state is determined. The electric power steering apparatus according to claim 1, further comprising: a torque determination unit. The reverse input detection means further includes:
Steering speed information acquisition means for acquiring information representing the steering speed;
Speed determining means for determining that the reverse input state is obtained when the steering speed is higher than a reference speed set at a high speed that cannot be rotated by a driver's steering operation from the acquired information. The electric power steering apparatus according to claim 1 or 2.

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